The present invention relates to disposable diaper and a method for incorporation of elastic members into such diaper. More particularly, the present invention relates to a construction of elastic members functioning to fit both side flaps of the disposable diaper of underpant type around infant's thighs and a method to incorporate such elastic members into said diaper.
The elastic members functioning to fit both side flaps of the disposable diaper around infant's thighs has already been adopted by the well known disposable diapers of underpant type and the most typical one of such diapers of prior art has been disclosed by U.S. Pat. No. 3,860,003. Usually, a single rubber tape has been incorporated into each side flap of the diaper as the elastic member. However, the diaper incorporated with such elastic members of single rubber tape type exerts a localized or linear high pressure around infant's thighs with linear pressure marks remaining around infant's thighs and sometimes causes a pain for the infant who wears such diaper particularly when the infant wears this for a relatively long period.
To eliminate such drawback, it has already been proposed to use the rubber tape which is formed relatively wide, as said elastic member. However, use of the rubber tape formed in such manner would be disadvantageous in the following aspect.
In view of the molding technique, it is difficult to obtain a rubber tape substantially thinner than the rubber tape which has usually been used as said elastic member and it would be almost impossible to obtain the rubber tape of uniform thickness even if molding of extremely thin rubber tape is possible. Accordingly, if the conventional rubber tape used as the elastic member is formed wider and incorporated into the diaper at the stretching ratio similar to that as used with the conventional rubber tape, a pressure around infant's thighs would be excessive, since the tensile stress thereof is too high. To obtain an elastic member having a tensile stress which is regarded optimal for a pressure to be exerted around infant's thigh, therefore, it is necessary to reduce the stretching ratio of said elastic member by a quantity corresponding to an increased width of said elastic member. This would result in an increase of cost due to an additional quantity of material for the elastic member required to enlarge the width thereof as well as due to an additional quantity of material for said elastic member required to reduce the stretching ratio thereof. Such increased cost is seriously disadvantageous for the disposable diaper which should be manufactured at a reasonably low cost.
It is certainly possible to overcome this drawback when several fine rubber strings are used as the elastic member, as will be understood from reading a further later description on the present invention. However, such a measure confronts a difficulty, namely, the disposable diaper must be mass-produced at a low cost and the rubber strings must be secured, by means of adhesive, to a backsheet comprising plastic film or the like and/or to a topsheet comprising nonwoven fabric or the like, both sheets being constituent members of the diaper. Furthermore, said drawback can be effectively overcome only when said rubber strings used as the elastic member are substantially finer than the rubber tape conventionally used as said elastic member of the diaper. However, finer the rubber strings to be used as the elastic member are and more the number of these rubber strings is, more difficult the handling of these rubber strings for securing them to said sheet(s) by means of adhesive and the operational efficiency is inevitably reduced.
An object of the present invention is, therefore, to provide an improved disposable diaper provided with elastic members respective comprising several rubber strings substantially finer the rubber tapes conventionally used as the elastic members of the disposable diaper and arranged at appropriate intervals in parallel within side flaps of the diaper so as to form several elastically stretchable lines in the respective side flaps and thereby to make good fit of said side flaps around infant's thighs.
Another object of the present invention is to provide an improved disposable diaper in which a plurality of extremely fine rubber strings arranged at appropriate intervals in parallel are used as the elastic members as previously mentioned so that the stretching ratio of these rubber strings may be increased while the length of these rubber strings to be used may be reduced with respect to the conventional rubber tapes commonly used as the elastic members in the disposable diapers of prior art and, as a result, the quantity of rubber material used for these elastic members may be sufficiently reduced to achieve production of the diaper at a low cost.
Still another object of the present invention is to provide an improved method for incorporation of said plurality of rubber strings serving as the elastic members into associated components of the disposable diaper comprising steps of continuously feeding these rubber strings, particularly, those in the form of respective single rubber tapes held by apparent side-by-side joints each having an intrinsic separability to said associated components while separating them into a predetermined number of rubber strings in neat order, and then securing these rubber strings to said components by adhesive so that the desired incorporation of these rubber strings into the diaper may be achieved at a high efficiency.
The other objects of the present invention will be apparent from the following description of the invention.